Using shared secret data (SSD) to authenticate between a CDMA network and a GSM network

ABSTRACT

A general global gateway (GGG) uses shared secret data to authenticate between a CDMA network and a GSM network such that a mobile station having a subscription in a GSM network can roam into a CDMA network and be authenticated to use the CDMA network without having a complete ANSI-41 subscription. The goal of authenticating a GSM subscriber in an ANSI-41 network using GSM authentication credentials is achieved by substituting encryption key Kc as SSD-A in the standard ANSI-41 computation of AUTHR using a CAVE algorithm.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 60/455, filed Mar. 18, 2003, and U.S. application Ser. No.10/804,267 filed Mar. 18, 2004, which are incorporated herein byreference in their entirety.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

“Internetworking Between A First Network And A Second Network” by NikhilJain, having Ser. No. 10/804,265 and “Authenticating Between A CDMANetwork And A GSM Network,” having Ser. No. 10/804,301 and “Using SharedSecret Data (SSD) to Authenticate Between a CDMA Network and a GSMNetwork” having Ser. No. 10/804,267, filed concurrently herewith andassigned to the assignee hereof, and which is expressly incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationsystems, and more particularly to systems that permit authenticatingbetween a CDMA network and a GSM network.

BACKGROUND

Code division multiple access (CDMA) is a digital wireless technologythat inherently has relatively greater bandwidth capacity, i.e., thatinherently permits the servicing of more telephone calls per frequencyband, than other wireless communication technologies. Moreover, thespread spectrum principles of CDMA inherently provide securecommunications. U.S. Pat. No. 4,901,307, incorporated herein byreference, sets forth details of a CDMA system, which can be used totransmit both voice calls and non-voice computer data.

Despite the advantages of CDMA, other wireless systems exist that useother principles. For example, in much of the world GSM is used, whichemploys a version of time division multiple access.

Whether CDMA principles or other wireless principles are used, wirelesscommunication systems can be thought of as having two main components,namely, the wireless radio access network (RAN) and the coreinfrastructure which communicates with the RAN and with externalsystems, such as the public switched telephone network (PSTN), theInternet (particularly although not exclusively for data calls), etc.The core infrastructures associated with the various wirelesstechnologies can be very expensive, both in terms of hardware and interms of developing communication protocols to support particularized,typically system-specific call switching, subscription and attendantauthentication and call monitoring, and billing. Consequently, thecommunication protocols of one wireless system (in the case of GSM, GSMprotocols, and in the case of CDMA such as cdma2000-1x, IS-41 protocols)may not be compatible with those of another system without expensivelyprohibitive alterations in the core infrastructure of one system or theother.

It would be desirable to internetwork between a CDMA network and a GSMnetwork, thereby enabling the use of a CDMA-based RAN, with itsattendant advantages, and enabling the use of a GSM-based coreinfrastructure, since GSM is extant in much of the world.

Thus, a dual-mode mobile station may be enabled to advantageouslyinterface with a GSM core infrastructure when in, e.g., Europe, and touse a CDMA infrastructure when in, e.g., the United States.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method of wirelesscommunications between a first network and a second network enabling amobile station (MS) subscribed in the first network to communicate usingthe second network, comprises storing an identity of the mobile station,obtaining authentication information from the first network based on theidentity of the mobile station, storing the authentication informationfrom the first network in a general global gateway (GGG), using analgorithm using the authentication information to produce an encryptionkey, and using the encryption key to authenticate the mobile station.

It is understood that other embodiments of the present invention willbecome readily apparent to those skilled in the art from the followingdetailed description, wherein various embodiments of the invention areshown and described by way of illustration. As will be realized, theinvention is capable of other and different embodiments and its severaldetails are capable of modification in various other respects, allwithout departing from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a wireless communications systemcomprising a CDMA network, a GSM network, General Global Gateway (GGG),and mobile stations;

FIGS. 2 a and 2 b shows a flowchart for authenticating a CDMA mobilestation with a subscription in a GSM network in accordance with anembodiment not using SSD;

FIG. 3 depicts the standard ANSI-41 approach to producingauthentication;

FIG. 4 shows the authenticating of a GSM subscriber in an ANSI-41network using GSM authentication credentials by using Kc as SSD-A inaccordance with an embodiment;

FIG. 5 shows the information flow for a successful SSD update procedurein which the GGG updates the SSD shared with the serving MSC/VLR inaccordance with an embodiment;

FIG. 6 shows an initial registration scenario modified for SSD sharingin accordance with an embodiment; and

FIG. 7 shows the information flow for a successful registration with anew MSC/VLR when SSD sharing is allowed in accordance with anembodiment.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a wireless communications system 10comprising a CDMA network 12, a GSM network 14, General Global Gateway(GGG) 16, and mobile stations 18, 20, 22, 24. GSM mobile station 20includes a Subscriber Identity Module (SIM) 26. CDMA mobile station 24includes SIM 28. SIMs 26, 28 are removable engaged with mobile stations20, 24, respectively, in accordance with principles known in the art. Inan embodiment, the GGG is a GSM Global Gateway.

The GGG 16 internetworks between the CDMA network 12 and the GSM network14. The GGG includes a transceiver (not shown) that allows it to sendand receive messages to and from the CDMA network 12 and the GSM network14.

In an embodiment, the CDMA network is an ANSI-41 network. It would beapparent to those skilled in the art, the CDMA network 12 may be anyvariety of CDMA networks including, but not limited to cdma2000-1x andcdma2000-1xEV-DO. It would also be apparent to those skilled in the art,the GSM network 14 may be any variety of GSM network or successornetwork including, but not limited to General Packet Radio Services(GPRS), Universal Mobile Telecommunication System (UMTS), andWideband-CDMA (W-CDMA).

The GSM network 14 comprises a GSM Core 30 and a GSM Radio AccessNetwork 32. The GSM Core 30 comprises a GSM Home Location Register (GSMHLR) 34, a GSM Authentication Center (GSM AuC) 36, a GSM Short MessageCenter (GSM SMSC) 38 and a GSM Gateway Mobile Switching Center (GSMGMSC) 40. The CDMA network 12 comprises a a CDMA Home Location Register(CDMA HLR) 42, a CDMA Authentication Center (CDMA AuC) 44, CDMA MSC 46and associated CDMA Radio Access Network (CDMA RAN) 48.

With respect to a GSM mobile station with a subscription in a CDMA Core20, the GGG 16 functions as a Visitor Location Register (VLR) 50 to theGSM network 14. With respect to a CDMA mobile station 24 with asubscription in a GSM Core 30, the GGG 16 functions as a VisitorLocation Register (Visitor LR) 52 to the CDMA network 12.

Mobile stations 18, 20, 22, 24 do not need to have a subscription inboth core infrastructures 12, 14 and may have a subscription in only oneof the core infrastructures 12, 14.

With respect to both the GSM mobile station with a subscription in aCDMA Core 20 and a CDMA mobile station with a subscription in a GSM Core24, the GGG 16 functions as a Short Message Service Center (SMSC) 54. Itwould be apparent to those skilled in the art that the GGG 16 caninclude or communicate with the SMSC 54.

Mobile stations 18, 20 support a GSM signaling protocol, a GSMAuthentication procedure, and a GSM Short Message Service. Likewise,mobile stations 22, 24 support a CDMA signaling protocol, a CDMAAuthentication procedure, and a CDMA Short Message Service.

During registration of a CDMA mobile station with a subscription in theGSM core 24, the GGG acts as an Authentication Controller in a CDMAnetwork, but authenticates the mobile station 24 using the GSMauthentication mechanism. Likewise, during registration of a GSM mobilestation with a subscription in the CDMA core 20, the GGG acts as anAuthentication Controller in a GSM network, but authenticates the mobilestation 20 using the CDMA authentication mechanism.

The GGG acts as a message center via Short Message Service Center 54. Ina CDMA network, SMS messages are routed to and from the mobile station24 using a CDMA SMS mechanism. In other words, in a CDMA network, GSMmessages are tunneled to and from mobile station 24 using a CDMA SMSmechanism. The GSM messages are encapsulated within CDMA SMS messages.

Likewise, in a GSM network, SMS messages are routed to and from themobile station 20 using a GSM SMS mechanism. In other words, in a GSSMnetwork, CDMA messages are tunneled to and from mobile station 20 usinga GSM SMS mechanism. The CDMA messages are encapsulated within GSM SMSmessages.

An incoming call to a registered GSM subscriber 24 arrives at GSMgateway MSC (GSM GMSC) 40 in the subscriber's home GSM network 14. TheGMSC 40 interrogates the GSM LR 50 to determine the location of thesubscriber 24, which is in the CDMA network 12. The location of the GSMsubscriber 24 from the perspective of the GSM LR 50 is in the GGG 16,which appears as a GSM VLR. When the GSM LR 50 requests routinginformation from the GGG 16, the GGG 16 requests routing informationfrom the serving CDMA LR 52 and thus the call is routed to the CDMA MSC46.

Likewise, an incoming call to a registered CDMA subscriber 20 arrives atCDMA MSC 46 in the subscriber's home CDMA network 12. The CDMA MSC 46interrogates the CDMA LR 52 to determine the location of the subscriber20, which is in the GSM network 14. The location of the CDMA subscriber20 from the perspective of the CDMA LR 52 is in the GGG 16, whichappears as a CDMA VLR. When the CDMA LR 50 requests routing informationfrom the GGG 16, the GGG 16 requests routing information from theserving GSM LR 50 and thus the call is routed to the GSM GMSC 40.

The CDMA-based mobiles stations 22, 24 communicate with a CDMA mobileswitching center (MSC) 46 using a CDMA radio access network (RAN) 48 inaccordance with CDMA principles known in the art. In an embodiment, theCDMA MSC 46 is an IS-41 MSC.

Likewise, the GSM-based mobiles stations 18, 20 communicate with a GSMmobile switching center (GSM GMSC) 40 using a GSM RAN 32 in accordancewith GSM principles known in the art.

In accordance with CDMA principles known in the art, the CDMA RAN 48includes base stations and base station controllers. In an embodiment,CDMA RAN 24 shown in FIG. 1 uses cdma2000, and specifically uses eithercdma2000 1x, cdma2000 3x, or cdma2000 high data rate (HDR) principles.

In accordance with GSM principles known in the art, the GSM RAN 32includes base stations and base station controllers. In an embodiment,GSM RAN 32 uses either GSM, GPRS, EDGE, UMTS, or W-CDMA principles.

The CDMA core infrastructure comprising the CDMA MSC 46 and CDMA RAN 48can include or can access a CDMA authentication center (CDMA AUC) 44 anda CDMA home location register (CDMA HLR) 42 in accordance with CDMAprinciples known in the art to authenticate subscriber mobile station22, and to collect accounting and billing information as required by theparticular CDMA core infrastructure.

Likewise, the GSM core 30 can include or can access a GSM authenticationcenter (GSM AUC) 36 and a GSM home location register (GSM HLR) 34 inaccordance with GSM principles known in the art to authenticatesubscriber mobile station 18, and to collect accounting and billinginformation as required by the particular GSM core infrastructure.

The CDMA MSC 46 uses the GGG 16 to communicate with the GSM network 14.The GSM network 14 can include or can access a GSM authentication center36 and a GSM home location register (HLR) 34 in accordance with GSMprinciples known in the art to authenticate subscriber mobile station 24and to collect accounting and billing information as required by theparticular GSM core 30.

Likewise, GSM GMSC 40 uses the GGG 16 to communicate with the CDMAnetwork 12. The CDMA network 12 can include or can access a CDMAauthentication center 44 and a CDMA home location register (HLR) 42 inaccordance with CDMA principles known in the art to authenticatesubscriber mobile station 20 and to collect accounting and billinginformation as required by the particular CDMA network 12.

Both the GSM core 30 and the CDMA core infrastructure can communicatewith a network such as a public switched telephone network (PSTN) and/oran Internet Protocol (IP) network.

With respect to a CDMA mobile station 24 with a subscription in a GSMCore 30, the GGG 16 functions as a VLR 50 to the GSM network 14. The GGGmeets GSM protocol requirements for a VLR 50. The GGG interacts with GSMcore network elements such as GSM HLR 34 and GSM SMSC 38 according toGSM specifications, except that the GGG 16 routes incoming calls to theCDMA network 12. The GSM LR 50 also performs a location update with theGSM network 14 when the mobile station registers in the CDMA network 12.In this sense, the GGG acts as a VLR to the whole CDMA network 12.

With respect to a GSM mobile station 20 with a subscription in a CDMAnetwork 12, the GGG 16 functions as a VLR 52 to the CDMA network 14. TheGGG meets CDMA protocol requirements for a VLR 52. The GGG interactswith CDMA core network elements such as CDMA HLR 42 and CDMA MSC 46according to CDMA specifications, except that the GGG 16 routes incomingcalls to the CDMA network 12. The CDMA LR 52 also performs a locationupdate with the CDMA network 12 when the mobile station registers in theGSM network 14. In this sense, the GGG acts as a VLR to the whole GSMnetwork 14.

When a mobile station that is in the CDMA network 12 is called from theGSM network 14, the call is routed to the CDMA LR 52 in the GGG 16 perstandard specifications. The GGG 16 routes the call to the CDMA network12. The CDMA network 12 eventually routes the call to the CDMA MSC 46serving the mobile station. Similarly, if an SMS is routed to the CDMAnetwork 12 from the GSM network 14, the GGG 16 routes the message to amessage center (not shown) within the CDMA network 12.

When a mobile station that is in the GSM network 14 is called from theCDMA network 12, the call is routed to the GSM LR 50 in the GGG 16 perstandard specifications. The GGG 16 routes the call to the GSM network14. The GSM network 14 eventually routes the call to the GSM GMSC 40serving the mobile station. Similarly, if an SMS is routed to the GSMnetwork 10 from the CDMA network 12, the GGG 16 routes the message to aGSM SMSC 38 within the GSM network 14.

When a mobile station registers with the CDMA network 12, the CDMAnetwork 12 sends a location update indication to the GSM network 14. TheGSM LR 50 then performs a location update as per standard specificationswith the GSM core network 14.

When a mobile station registers with the GSM network 14, the GSM network14 sends a location update indication to the CDMA network 12. The CDMALR 52 then performs a location update as per standard specificationswith the CDMA network 12.

With respect to a CDMA mobile station 24 with a subscription in a GSMCore 30, the GGG 16 acts as an HLR 52 in the CDMA network 12. The CDMALR 52 shall meet HLR protocol requirements for GSM to CDMA roaming. Animportant piece of information that the HLR 50 maintains is the addressof the CDMA MSC 46 serving the mobile station 24. When the GSM LR 50 inthe GGG 16 routes a call to the CDMA side 12, the CDMA LR 52 willfurther route it to the serving MSC 46.

With respect to a GSM mobile station 20 with a subscription in a CDMAnetwork 12, the GGG 16 acts as an HLR 50 in the GSM network 14. The GSMLR 50 shall meet HLR protocol requirements for CDMA to GSM roaming. Animportant piece of information that the HLR maintains is the address ofthe GSM GMSC 40 serving the mobile station 20. When the CDMA LR 52 inthe GGG 16 routes a call to the GSM side 14, the GSM LR 50 will furtherroute it to the serving MSC 40.

The GGG acts as an Authentication Controller (AUC) in the CDMA networkfor GSM subscribers 24. The AUC 44 in a CDMA network 12 is responsiblefor authenticating a mobile station and permitting/denying access tonetwork resources. The AUC function in the GGG does not call for A-keyprovisioning at the GGG or the MS. Instead the GGG uses the GSMauthentication credentials and the GSM authentication method via GSMsignaling to authenticate the mobile station 24. The GGG responds tovalid messages that can be received by a CDMA AUC 44.

The GGG acts as an Authentication Controller (AUC) in the GSM networkfor CDMA subscribers 20. The AUC 36 in a CDMA network 14 is responsiblefor authenticating a mobile station and permitting/denying access tonetwork resources. The AUC function in the GGG does not call for A-keyprovisioning at the GGG or the MS. Instead the GGG uses the CDMAauthentication credentials and the CDMA authentication method via CDMAsignaling to authenticate the mobile station 20. The GGG responds tovalid messages that can be received by a GSM AUC 36.

The GGG 16 acts as a Message Center (MC) in the CDMA network 12 androutes SMS messages between the CDMA mobile station 24 and GSM GMSC 40using a GSM SMS mechanism.

Likewise, the GGG 16 acts as a Message Center (MC) in the GSM network 14and routes SMS messages between the GSM mobile station 20 and CDMA MSC46 using a CDMA SMS mechanism.

The CDMA MS 24 is required to have a valid identity in the CDMA network.If this identity is different from the GSM International MobileSubscriber Identity (IMSI) (i.e., if the CDMA network does not use trueIMSI), then the GGG provides a mapping between the CDMA identity and theGSM IMSI. It would be apparent to those skilled in the art that anytechnique/method known in the art to uniquely identify the mobilestation 24 may be used.

The GSM MS 20 is required to have a valid identity in the GSM network.In an embodiment, this identity is a GSM IMSI (i.e., if the CDMA networkdoes not use true IMSI). If the identity in the GSM network is differentfrom the identity in a CDMA network, then the GGG provides a mappingbetween the GSM identity and the CDMA identity. It would be apparent tothose skilled in the art that any technique/method known in the art touniquely identify the mobile station 20 may be used.

In a non-limiting embodiment, mobile stations 18, 20, are mobiletelephones made by Kyocera, Samsung, or other manufacturer that use GSMprinciples and GSM over-the-air (OTA) communication air interfaces. In anon-limiting embodiment, mobile stations 22, 24, are mobile telephonesmade by Kyocera, Samsung, or other manufacturer that use CDMA principlesand CDMA over-the-air (OTA) communication air interfaces. The presentinvention, however, applies to other mobile stations such as laptopcomputers, wireless handsets or telephones, data transceivers, or pagingand position determination receivers. The mobile stations can behand-held or portable as in vehicle-mounted (including cars, trucks,boats, planes, trains), as desired. However, while wirelesscommunication devices are generally viewed as being mobile, it is to beunderstood that the present invention can be applied to “fixed” units insome implementations. Also, the present invention applies to datamodules or modems used to transfer voice and/or data informationincluding digitized video information, and may communicate with otherdevices using wired or wireless links. Further, commands might be usedto cause modems or modules to work in a predetermined coordinated orassociated manner to transfer information over multiple communicationchannels. Wireless communication devices are also sometimes referred toas user terminals, mobile stations, mobile units, subscriber units,mobile radios or radiotelephones, wireless units, or simply as “users”and “mobiles” in some communication systems.

FIGS. 2 a and 2 b shows a flowchart for authenticating a CDMA mobilestation 24 with a subscription in a GSM network 14 in accordance with anembodiment not using SSD. FIGS. 2 a and 2 b are described as they informthe description of FIG. 6.

In step 202, mobile station 24 (MS) roams into a CDMA area and the flowof control proceeds to step 204. In step 204, the mobile station 24initiates a registration system access to a CDMA MSC 46 via a CDMA RAN48 and the flow of control proceeds to step 206.

The registration system access is a message to the CDMA MSC 46 via theCDMA RAN 48, the message including an identity of the mobile station 24.In an embodiment, the identity of the mobile station 24 may be providedby the SIM 28. In an embodiment, the identity of the mobile station 24is an IMSI. In an embodiment, the identity of the mobile station 24 is aMobile Identification Number (MIN).

In step 206, the CDMA MSC 46 determines, based on the mobile stationidentity, whether the mobile station 24 is a GSM subscriber. In anembodiment, wherein the identity of the mobile station 24 is an IMSI,the MSC 46 can make this determination because the IMSI contains, amongother information, a code representing the country and network in whichthe mobile station has a subscription.

In the event that the CDMA-subscribing mobile station 22 is the mobilestation under test, the flow of control proceeds to step 208. In step208, the mobile station 22 is authenticated using CDMA principles by theCDMA core infrastructure, using the CDMA HLR 42 and CDMA AUC 44.

In the event that the CDMA mobile station 24 with a subscription in theGSM network 14 is the mobile station under test, the flow of controlproceeds to step 210. In step 210, the CDMA MSC 46 accesses the GGG 16by sending an Authentication Request to the CDMA LR 52 in the GGG 16 andthe flow of control proceeds to step 212 in accordance with anembodiment. In another embodiment, the flow of control proceeds to step214.

In an embodiment, the identity of the mobile station 24 is sent to theCDMA LR 52 as part of the Authentication Request. Alternatively, theidentity of the mobile station 24 is sent to the CDMA LR 52 in additionto the Authentication Request.

In an embodiment, the Authentication Request may include parameters MIN,ESN and COUNT. ESN is an electronic serial number.

In an embodiment, the Authentication Request may include parameters MIN,ESN and COUNT. ESN is an electronic serial number. COUNT represents acount of a predetermined event that is a mutually agreed upon eventbetween the GGG 16 and mobile station 24. In an embodiment, the GGG 16shares the updating of COUNT with a node that interacts with the GGG 16.By sharing the update function with another node, the message trafficbetween the GGG 16 and the other node may be reduced. For example, ifthe GGG 16 shares the function of updating COUNT with the CDMA MSC 46,then the message traffic between the GGG 16 and the CDMA MSC 46 may bereduced.

In an embodiment, COUNT represents the number of times a mobile station24 attempts to access the GSM network 14. Each time the mobile station24 accesses the GSM network, the GGG updates a COUNT for the particularmobile station 24. The mobile station 24 also updates its own COUNT forthe number of times it accesses the GSM network 14. The GGG 16 storesthe value of the ESN. In another embodiment, COUNT represents a numberof requests for authentication by the mobile station. It would beapparent to those skilled in the art that there are many events that canbe counted, which the mobile station 24 and GGG 16 can count.

In step 212, the GGG 16 compares the value of COUNT to a count value ina GGG database. If the value of COUNT is equal to the count value in theGGG database, then the flow of control proceeds to step 214. If thevalue of COUNT is not equal to the count value in the GGG database, thenthe flow of control proceeds to step 216. It would be apparent to thoseskilled in the art that depending on an application, a variety ofcriteria may be applied to determine whether an Authentication Requestis honored.

In step 214, an Authentication Request Return Result (ARRR) is set totrue and the flow of control proceeds to step 218. The AuthenticationRequest Return Result message indicates the result of the AuthenticationRequest.

In step 216, the Authentication Request Return Result is set to falseand the flow of control proceeds to step 220.

In response to the Authentication Request Return Result being true, theGGG 16 accesses the GSM network 14 and obtains necessary authenticationinformation from the GSM HLR 34 and GSM AuC 36. In step 218, the GGG 16looks up the MIN in its database to obtain a corresponding GSM IMSI andaccesses the GSM network 14 by sending a GSM HLR authentication messagewith the IMSI of the mobile station 24 to the GSM HLR/AuC 34, 36, inaccordance with an embodiment. The flow of control proceeds to step 220.

Method steps can be interchanged without departing from the scope of theinvention. Thus, it would be apparent to those skilled in the art thatstep 218 does not have to be performed before step 220.

In step 220, the GGG 16 sends the Authentication Request Return Resultto the CDMA MSC 46 and the flow of control proceeds to step 222. In step222, the Authentication Request Return Result is tested. If theAuthentication Request Return Result is true, then in step 224 the GGG16 starts a timer, T_(REG) and the flow of control proceeds to step 226.

If the Authentication Request Return Result is false, then the flow ofcontrol proceeds to step 228. In step 228, the CDMA MSC 46 sends amobile station authentication message to the mobile station 24indicating the mobile station 24 is not authenticated. It would beapparent to those skilled in the art that the mobile station mayreattempt authentication depending on the application.

The GGG includes a logic unit (not shown) to execute program logic. Itwould be apparent to those skilled in the art that the logic unit mayinclude a general purpose processor, a special-purpose processor, and/orfirmware.

In step 226, the CDMA MSC 46 upon receiving an Authentication RequestReturn Result indicating successful authentication, sends a RegistrationNotification to the CDMA LR 52 in the GGG 16. The flow of controlproceeds to step 230.

In step 230, a check is made to determine whether the GGG 16 receivedthe Registration Notification before T_(REG) expired. If the GGG 16received the Registration Notification before T_(REG) expired, then theflow of control proceeds to step 232, otherwise the flow of controlproceeds to step 234. In step 232, Registration Notification ReturnResult is set to indicate T_(REG) did not expire and the flow of controlproceeds to step 236. In step 234, Registration Notification ReturnResult is set to indicate T_(REG) expired and the flow of controlproceeds to step 236.

In step 236, the GGG 16 responds to the Registration Notification with aRegistration Notification Return Result indicating whether T_(REG)expired. The Registration Notification Return Result is sent from theGGG 16 to the CDMA MSC 46.

In an embodiment, the GGG 16 sends a message with or within theRegistration Notification Return Result indicating SMS only mode/status.“SMS only” means the mobile station 24 sends and receives only SMSmessages, not data and/or voice messages. The flow of control proceedsto step 238.

In step 238, the CDMA MSC 46 sends a Registration Accept message to themobile station 24 upon receiving the Registration Notification ReturnResult. Like the Registration Notification Return Result, theRegistration Accept message indicates whether T_(REG) expired. The flowof control proceeds to step 240.

In step 240, the mobile station 24 determines whether the RegistrationAccept message indicates an accepted registration, i.e., T_(REG) did notexpire. If T_(REG) expired, then the flow of control proceeds to step242, otherwise the flow of control proceeds to step 244.

In step 242, the mobile station 24 may or may not reattemptregistration. It would be apparent to those skilled in the art thatdepending on a mobile station application, the mobile station may or maynot reattempt registration.

Method steps can be interchanged without departing from the scope of theinvention. Thus, it would be apparent to those skilled in the art thatstep 244 does not have to be performed after step 242.

Step 244 only has to be executed after the GSM HLR authenticationmessage has been sent to the GSM HLR/AuC 34, 36 of step 218. In step244, the GSM HLR/AuC 34, 36 sends a GGG authentication message includingauthentication parameters to the GGG 16 and the flow of control proceedsto step 246.

After the GGG 16 successfully sends the Registration Notification ReturnResult to the CDMA MSC 46 and receives the GGG authentication messagefrom the GSM HLR/AuC 34, 36, the GGG 16 sends a GSM authenticationrequest message to the CDMA MSC 46 in step 246. The flow of controlproceeds to step 248. In step 248, the CDMA MSC 46 forwards the GSMauthentication request message to the mobile station 24 and the flow ofcontrol proceeds to step 250.

In an embodiment, an application may have more criteria forauthenticating mobile stations apart from the criteria applied to theoriginal Authentication Request of step 210. Thus, in an embodiment, theCDMA MSC 46 sends a second authentication request (not shown) to the GGG16 and the GGG 16 responds to the second authentication request (notshown).

In step 250, the mobile station 24 responds to the GSM authenticationrequest message by determining authentication parameters such as anencryption key using a GSM authentication method and sending anauthentication response including the authentication parameters to theCDMA MSC 46. In an embodiment, the authentication response is sent usingthe IS-637 SMS transport. The flow of control proceeds to step 252.

In step 252, the CDMA MSC 46 forwards the authentication response to theGGG 16 and the GGG 16 validates that the authentication parameters bymatching the authentication parameters to values received from the GSMHLR/AuC 34, 36 in step 244. The flow of control proceeds to step 254.

In step 254, the GGG 16 sends an update location message to the GSM HLR34 to update the location of the mobile station 24 and the flow ofcontrol proceeds to step 256. In step 256, the GSM HLR 34 sends GSMsubscriber profile data of the mobile station 24 to the GSM LR 50 in theGGG 16. The flow of control proceeds to step 258.

In step 258, the GGG 16 maps the GSM subscriber profile data to a CDMAsubscriber profile and sends the CMDA profile data in a QualificationDirective to the CDMA MSC 46 and the flow of control proceeds to step260. The Qualification Directive indicates that the mobile station 24 isqualified, i.e., authorized to communicate with the GSM network 14. Ifthe mobile station 24 is not qualified, then mobile station 24 is notauthorized to communicate with the GSM network 14 (not shown). In anembodiment, the GGG 16 indicates to the CDMA MSC 46 “full profile,”which in turn is forwarded to the mobile station 24 and indicates to themobile station 24 that the mobile station 24 can send and receivewithout being limited to SMS messages.

In step 260, the CDMA MSC 46 responds to the Qualification Directive andsends a Qualification Directive Response to the CDMA LR 52 and the flowof control proceeds to step 262.

In step 262, responsive to the GSM LR 50 receiving the GSM subscriberprofile data, the GGG 16 sends a GSM subscriber profile data response tothe GSM HLR/AuC 34, 36.

In step 264, responsive to the GSM HLR 34 receiving the update locationmessage from the GGG 16 in step 254, the GSM HLR 34 responds to theupdate location message and sends a update location message response tothe GSM LR 50, the update location message response indicating that thelocation of the mobile station 24 has been updated at the GSM LR 50.

Authentication Keys

It is in the area of authentication that the GGG differs most from theJ-STD-038 IIF. Since the J-STD-038 IIF requires that the roamingsubscriber have dual subscriptions—one for ANSI-41 and the other forGSM—it uses standard ANSI-41 techniques to authenticate the subscriberin ANSI-41 foreign mode. In contrast, the GGG solution does not requirethat the ANSI-41 foreign mode roamer have a complete ANSI-41subscription. In particular, either the MS or GGG needs to beprovisioned with ANSI-41 A-keys. The following first describes thestandard ANSI-41 authentication mechanism. Then modifications to ANSI-41method are described.

Standard ANSI-41 Authentication

The standard ANSI-41 approach to producing authentication keys isdepicted in FIG. 3. The A-key (which is the secret data known only tothe mobile station and authentication center) and a random number calledRANDSSD are processed using a CAVE algorithm to produce a 128-bit numbercalled the Secret Shared Data (SSD). This operation is performed in themobile station and the authentication center. The SSD consists of a64-bit SSD-A key used for authentication and a 64-bit SSD-B key used forencryption. On each system access the mobile station generates anauthentication response (AUTHR) by processing SSD-A, ESN, MIN,authentication data (AUTH_DATA—either IMSI_S or dialed digits dependingon the system access type) and a random number (RAND) broadcast by theRAN in overhead messages. The processing is performed again by executingthe CAVE algorithm. The mobile station transmits AUTHR in the systemaccess and is authenticated when the authentication center (oroptionally the MSC/VLR) independently performs the same computation andcompares the result with that received.

Using Kc as SSD-A

The goal of authenticating a GSM subscriber in an ANSI-41 network usingthe GSM authentication credentials can be achieved by using Kc as SSD-A.The new method to generate the SSD-A key and AUTHR in accordance with anembodiment is shown in FIG. 4. When the GSM authentication is run at themobile station and at the GSM AuC, the secret key Ki (known only to thesubscriber's SIM and the GSM AuC) and the random number (GSM_RAND) areused to produce the SRES and the encryption key Kc. Kc is 64 bits inlength just as SSD-A. Therefore, Kc can be substituted for the SSD-Avalue in the standard ANSI-41 computation of AUTHR using a CAVEalgorithm.

Since the GGG gets the GSM authentication triplets (i.e., GSM_RAND, SRESand Kc) from the GSM AuC and the RAND, ESN, MIN and AUTH_DATA in anAuthenticationRequest INVOKE it can then use the Kc value as the SSD-Avalue to authenticate the mobile station using the ANSI-41 method afterthe mobile station is first authenticated using GSM_RAND. In otherwords, the GGG and the mobile station have a common value of Kc afterthe mobile station executes the GSM authentication procedure using thevalue of GSM_RAND at the GGG. This GSM authentication can be performedin the ANSI-41/CDMA2000 network using GSM signaling over IS-637 SMStransport. Once the mobile station and GGG have the same value of Kc,then this value can be used as SSD-A and standard ANSI-41 methods can beused to authenticate the mobile station. The advantage of using theANSI-41 authentication techniques is better signaling efficiency. Notethat this approach also meets the goal of authenticating a mobilestation in the ANSI-41 network using GSM credentials.

Authentication With SSD Sharing

For the operational scenarios of FIG. 2, the ANSI-41 AC in the GGGretains authentication responsibility. The serving MSC/VLR is assumed torespond to each mobile station access attempt (e.g., registration,origination, page response and flash) with an AuthenticationRequestINVOKE towards the ANSI-41 HLR/AC in the GGG. While this approachprovides maximum security, the tradeoff is more signaling trafficbetween the ANSI-41 MSC/VLR and the GGG.

To reduce MSC/VLR—HLR/AC signaling traffic, a method that allows the ACto distribute some authentication responsibility with the servingMSC/VLR is described below. SSD sharing is applied to a GGG-based GSM1xsolution if the value of Kc is used for SSD-A as described in referenceto FIG. 4. The remainder of this section describes how SSD sharing isperformed.

SSD Update

FIG. 5 shows the information flow for a successful SSD update procedurein which the GGG updates the SSD shared with the serving MSC/VLR inaccordance with an embodiment. The initial condition for this scenariois that the GGG has previously shared SSD with the serving MSC/VLR andthat the MSC/VLR authenticates the MS when it performs a system access.

The following procedure describes this information flow:

In step 501, the GGG initiates the SSD update by invoking AuthenticationDirective (IS41_AUTHDIR) towards the ANSI-41 MSC/VLR with the MIN, ESNand NOSSD parameters.

In step 502, the MSC/VLR discards the SSD that it has for the specifiedMS, and responds by invoking Authentication Directive Return Requesttowards the GGG. The MSC/VLR will now invoke Authentication Requesttowards the HLR/AC in the GGG for each system access of this MS.

In step 503, the GGG invokes Count Request (IS41_COUNTREQ) towards theMSC/VLR to request the current value of the CallHistoryCount (COUNT)parameter for the MS.

In step 504, the MSC/VLR responds with the Count Request Return Result(IS41_countreq), containing the requested COUNT parameter.

In step 505, if the GGG has no additional GSM authentication tripletsfor the MS, then the GGG invokes MAP_SEND_AUTHENTICATION_INFO towardsthe GSM HLR. The next time that the MS accesses the system, thefollowing steps occur:

In step 506, the GSM HLR responds with MAP_send_authentication_infocontaining a set (at least one) of authentication triplets.

In step 507, the next time the MS accesses the system, the followingoccurs:

In step 508, since SSD is no longer being shared, the MSC/VLR invokesAuthentication Request (IS41_AUTHREQ) towards the GGG to authenticatethe MS system access.

In step 509, the AC in the GGG executes ANSI-41 authentication given theparameters received in the previous step, and the value of Kc (SSD-A)stored for that MS. The AC then invokes Authentication Request ReturnResult (IS41_authreq) towards the MSC/VLR to indicate successful ANSI-41authentication.

In step 510, the GGG initiates the GSM1x authentication process byinvoking GSM1x Authentication Requests using the IS41_SMDPP transport.

In step 511, the MSC forwards this SMS to the MS.

In step 512, the MS responds to the GSM1x authentication request bycomputing SRES and Kc using the GSM authentication method, and sending aresponse (GSM1x Auth Rsp) using IS-637 SMS transport.

In step 513, the MSC forwards the SMS to the GGG, and the GGG validatesthat the SRES in the GSM1x Auth Rsp matches the value received from theGSM HLR/AuC. This step completes the SSD update to the MS.

In step 514, upon the next system access by the MS, the MSC/VLR invokesAuthentication Request (IS41_AUTHREQ) towards the GGG.

In step 515, the AC in the GGG executes ANSI-41 authentication given theparameters received in the previous step, and the value of Kc (SSD-A)stored for that MS. The AC then invokes Authentication Request ReturnResult (IS41_authreq) towards the MSC/VLR to indicate successful ANSI-41authentication. The SSD parameter is also included to share SSD with theMSC/VLR.

Initial registration with SSD sharing

FIG. 6 shows an initial registration scenario modified for SSD sharingin accordance with an embodiment. The information flow shown in FIG. 6is similar to the information flow shown in the flowchart of FIG. 2until step 619.

In step 601, the initial registration scenario begins when the MSperforms a registration system access.

In step 602, the ANSI-41 MSC/VLR invokes Authentication Request(IS41_AUTHREQ) towards the HLR in the GGG (the HLR for the GSM1x MS).The relevant parameters in this AUTHREQ are MIN, ESN and COUNT. The GGGstores the value of ESN and compares the value of COUNT to the value inthe database.

In step 603, the GGG looks up the MIN in its database to get thecorresponding GSM IMSI and invokes the MAP_SEND_AUTHENTICATION_INFO(Error! Reference source not found.) towards the GSM HLR/AuC.

In step 604, the GGG invokes the Authentication Request Return Result(IS41_authreq) towards the MSC/VLR indicating successful authenticationand starts a timer, TREG.

In step 605, upon receiving the IS41_authreq indicating successfulauthentication the MSC/VLR invokes Registration Notification(IS41_REGNOT) towards the HLR in the GGG.

In step 606, if the GGG receives the IS41_REGNOT before T_(REG) expires(as in this scenario), then it responds with a Registration NotificationReturn Result (IS41_regnot) with a profile macro authorizing SMS only.SMS only is specified as follows:

-   -   SMS_OriginationRestriction=“allow all”    -   SMS_TerminationRestriction=“allow all”    -   OriginationIndicator=“single directory number” (e.g., plays        announcement)

In step 607, upon receiving the IS41_regnot the MSC/VLR sendsregistration accept to the MS.

In step 608, the GGG receives the MAP_send_authentication_info from theGSM HLR/AuC containing one or more authentication triplets.

In step 609, after the GGG successfully sends the IS41_regnot to theMSC/VLR (6) and receives the MAP_send_authentication_info from the GSMHLR/AuC (8), it sends the GSM1x authentication request (GSM1x Auth Req)message using IS41_SMDPP transport.

In step 610, the MSC forwards this SMS to the MS.

In step 611, the MS responds to the GSM1x authentication request bycomputing SRES and Kc using the GSM authentication method and sending aresponse (GSM1X Auth Rsp) using IS-637 SMS transport.

In step 612, the MSC forwards the SMS to the GGG and the GGG validatesthat the SRES in the GSM1x Auth Rsp matches the value received from theGSM HLR/AuC.

In step 613, the GGG invokes MAP_UPDATE_LOC towards the GSM HLR toupdate the location of the MS.

In step 614, the GSM HLR invokes MAP_INSERT_SUB_DATA towards the GSM VLRin the GGG to send the subscriber profile.

In step 615, the GGG maps the GSM subscriber profile to an ANSI-41subscriber profile and sends this ANSI-41 profile to the MSC/VLR byinvoking Qualification Directive (IS41_QUALDIR).

In step 616, the MSC/VLR responds to the Qualification Directive of step615.

In step 617, The GGG responds to the MAP_INSERT_SUB_DATA of step 614.

In step 618, the GSM HLR responds to the MAP_UPDATE_LOC of step 613.

In step 619, upon the next system access by the MS the following stepsoccur:

In step 620, the MSC/VLR VLR invokes Authentication Request(IS41_AUTHREQ) towards the GGG.

In step 621, the AC in the GGG executes ANSI-41 authentication given theparameters received in the previous step and the value of Kc (SSD-A)stored for that MS. The AC then invokes Authentication Request ReturnResult (IS41_authreq) towards the MSC/VLR to indicate successful ANSI-41authentication. The SSD parameter is also included to share SSD with theMSC/VLR.

Registration at new MSC/VLR with SSD sharing

FIG. 7 shows the information flow for a successful registration with anew MSC/VLR when SSD sharing is allowed in accordance with anembodiment.

In step 715, upon the next system access by the MS the following stepsoccur:

In step 716, the MSC/VLR VLR invokes Authentication Request(IS41_AUTHREQ) towards the GGG.

In step 717, the AC in the GGG executes ANSI-41 authentication given theparameters received in the previous step and the value of Kc (SSD-A)stored for that MS. The AC then invokes Authentication Request ReturnResult (IS41_authreq) towards the MSC/VLR to indicate successful ANSI-41authentication. The SSD parameter is also included to share SSD with theMSC/VLR.

While the particular USING SHARED SECRET DATA (SSD) TO AUTHENTICATEBETWEEN A CDMA NETWORK AND A GSM NETWORK as herein shown and describedin detail is fully capable of attaining the above-described objects ofthe invention, it is to be understood that it is the presently preferredembodiment of the present invention and is thus representative of thesubject matter which is broadly contemplated by the present invention,that the scope of the present invention fully encompasses otherembodiments which may become obvious to those skilled in the art, andthat the scope of the present invention is accordingly to be limited bynothing other than the appended claims, in which reference to an elementin the singular is not intended to mean “one and only one” unlessexplicitly so stated, but rather “one or more”. All structural andfunctional equivalents to the elements of the above-described preferredembodiment that are known or later come to be known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited as a “step”instead of an “act”.

Method steps can be interchanged without departing from the scope of theinvention.

1. A mobile station, comprising: means for receiving a key from a firstnetwork; and means for substituting the first network key for anauthentication key used in an algorithm to authenticate the mobilestation.